The present invention relates to EMI/RFI shielding, and in particular to an EMI/RFI shield for adjacent devices in a cage.
In the electronics and computer industry today, cases which hold circuitry that create electromagnetic radiation are shielded to prevent emission of radiation referred to as EMI/RFI. Regulatory bodies set maximum emission levels at various frequencies. Devices failing emission level tests may not be sold. Electronic devices may also need to be shielded from electromagnetic radiation generated by devices outside their cases. In the personal computer (PC) industry, processor speeds are increasing. Electronic devices, such as PCs must meet strict guidelines in the United States and other countries on the amount of radiation they produce within a given radius. With such high processor speeds, it is getting more and more difficult to ensure that PCs meet the radiation emission guidelines. In addition to the increasing frequency of operation, electronic devices must be manufactured in a cost effective manner to remain profitable.
Personal computers are frequently upgraded in function by users which may require taking apart the computer, adding circuitry, and putting the computer back together. To make this easier for a user to do, most PCs have panels which can be removed, and devices such as disk drives, CD and DVD players inserted into a cage. In some PCs, multiple such devices are staked vertically adjacent to each other. Such devices typically have a gap between them that is a source of EMI/RFI leakage. A way of preventing such leakage, while still permitting a user to upgrade their systems is needed.
Complex and costly solutions such as gluing an additional shield to cover gaps are too expensive, add additional parts which make the manufacturing process longer, are expensive, and prevent case of upgrading by a user. Applying a conductive foam strip with adhesive backing on either the bottom surface of the top device surface, or on the top surface of the bottom device is also difficult for users to perform.
A string with conductive filaments is placed across an opening of an electronic cage at a point between two devices to be installed in the electronic cage. In one embodiment, the cage is a drive cage for a personal computer. The cage is positioned within the personal computer and the string is positioned at a point to fill a gap between two drives when installed in the cage.
In a further embodiment, the string comprises a twisted metal wire with conductive filaments woven into the wire. The filaments are of sufficient length to contact both drives. The spacing of the filaments is varied as desired. In one embodiment, the spacing is dependent on the frequency of the radiation generated within the personal computer. The filaments are approximately perpendicular to the string in one embodiment. The filaments are randomly oriented with respect to the devices in one embodiment, and consistently oriented within a desired angle with respect to the devices in a further embodiment. In still further embodiments, each string has multiple wire brushes to ensure consistent contact with adjacent devices.
In one embodiment, the cage is provided with a flange having opposing cut out or stamped out hook portions on each side of the cage. The string is provided with a loop on each end for hooking over the hooks to position the string as desired. In one embodiment, the string is partially elastic such that it is stretchable for installation over the opposing hooks. In yet a further embodiment, a spring is provided proximate one of the hooks for coupling to the string, allowing easier installation for a non elastic string.